Starch is a naturally occurring polymer made up of anhydroglucose units and is obtained by processing plant materials. The plant materials from which starch is derived include, but are not limited to, corn, wheat, potato, cassava, and rice. Of these plant materials, corn is one of the most commonly used sources for starch in North America.
Starch is composed of two main components: amylose and amylopectin. Amylose is a linear polymer of glucose linked with mostly α(1→4) glycosidic bonds. Amylopectin is a branched polymer of glucose linked with both α(1→4) and α(1→6) glycosidic bonds.
A digestion-resistant carbohydrate is a carbohydrate that resists digestion in the human body. Such digestion-resistant carbohydrates can be prepared by heat-treating starch at a high temperature in a process called dextrinization.
Dextrinization rearranges the molecular structure of starch to form indigestible branched structures. Through dextrinization, a portion of the normal α(1→4) glycosidic bonds in starch are converted to random (1→4), (1→3) and (1→2)-alpha or beta bonds. These chemical changes are described in “Modified Starches: Properties and Uses”, O. B. Wurzburg, CRC Press, Inc. 1986, pp. 33-34. The human digestive system can only effectively digest α(1→4) bonds and not the α(1→3) and α(1→2) glycosidic bonds. Thus, digestion-resistant carbohydrate remains undigested in the small intestine.
In addition to digestion-resistant carbohydrate, dextrins are also produced as intermediate products through the process of dextrinization. Dextrins are a group of low molecular weight carbohydrates that have the same general formula as starch, but are smaller and less complex.
Dextrins may be categorized as either pyrodextrins or maltodextrins according to the method of dextrinization. For example, pyrodextrins are dextrins that are prepared from acid hydrolysis and heat treatment. Maltodextrins are either dextrins that are prepared from acid hydrolysis followed by enzymatic hydrolysis of the acid hydrolysate or dextrins that are prepared from enzymatic hydrolysis during heating.
Dextrins are used for numerous industrial applications. Examples of relevant manufacturing areas include, but are not limited to, the adhesive industry, the paper industry, the pharmaceutical industry, the mining industry, the food industry, and the textile industry. More specifically, dextrins can be used in water soluble glues, printing inks, food products, substitutes for lactose, and adhesives (e.g. for postage stamps, envelopes, and wallpapers). In addition, some indigestible dextrins are used in fiber supplements. For example, dextrin is used to make digestion-resistant maltodextrin (e.g., Fibersol-2®, a registered trademark of Matsutani Chemical Industry Co., Ltd., Itami-shi Hyogo-ken, JAPAN).
In preparation of digestion-resistant carbohydrate in dextrin (indigestible dextrin), the degree of dextrinization depends for example, on the temperature employed, the speed of heating, the time of holding the starch at the selected temperature, and the type and amount of acid or catalyst that is used. This also results in the development of color due to carmelization reactions. Carmelization reactions are a diverse group of dehydration, fragmentation, and polymerization reactions whose reaction rates are dependent on temperature and pH (See, “Sugar Chemistry”, R. S. Shallenberger and G. G. Birch, AVI, 1975, pp. 167-177).
As a result of the dextrinization and carmelization reactions, dextrins can be distinguished according to their physical properties including, but not limited to, color and solubility in water. Types of dextrins include white dextrins, yellow dextrins, and British gums.
White dextrins may be prepared by heating starch at 79° C. to 121° C. in the presence of acid catalyst for 3 to 8 hours. Under these conditions, the starch is hydrolyzed, whereby the long chain of glucose units of the starch molecule is reduced considerably. White dextrins generally have a limited cold water solubility and a limited stability of solution. After cooling, a cooked, aqueous solution of white dextrins soon sets to a paste.
Yellow dextrins are prepared by heating starch at 120° C. to 220° C., with the addition of acid catalyst for 6 to 8 hours. As a result of a transglucosidation reaction, yellow dextrins have more of a branched structure compared to white dextrins. A transglucosidation reaction is considered to be a recombination of fragments resulting from the hydrolysis with free hydroxyl groups to produce branched structures. The branching increases as the heat conversions are carried out at higher temperatures, or as the reaction time increases. Furthermore, the yellow dextrins have a higher cold water solubility as well as a more hydrophilic character relative to white dextrins.
British gums are prepared by applying heat at a relatively high pH in comparison with the white and yellow dextrins. For example, British gums are prepared by heating starch at 135° C. to 218° C. in the absence of acid catalyst for 3 to 8 hours. As a result of the high temperatures employed, British gums are considerably darker in color than white dextrins.
Improvements in the standard of living have resulted in an increased interest in health and improved eating habits which, among other factors, have resulted in a lengthened average life span. Attention has therefore been directed to dietary fibers and oligosaccharides to enhance the functions of foods and livestock feeds, as these materials are known to alleviate constipation and other desired biological regulatory functions. Indigestible substances, like indigestible dextrins, exhibit various modes of behavior on the digestive tracts, producing physiological effects on the living body. First, in the upper digestive tract, indigestible dextrins slow the transport of food and delay the absorption of nutrients. Delayed absorption of sugar, for example, suppresses the rise in blood sugar value, consequently lowering insulin requirements. Further, excretion of bile is promoted, diminishing the sterol group in the body thereby lowering the cholesterol level in the serum. Other physiological effects through the endocrine system are also reported.
Indigestible substances are not digested or absorbed by the digestive tract, including the small intestine and eventually reach the large intestine. On reaching the large intestine, oligosaccharides, dietary fibers and indigestible dextrins are partly acted on by enterobacteria yielding short-chain fatty acids, intestinal gases, vitamins, etc. Acidification of the intestinal environment by the short-chain fatty acids condition the intestine. It has been reported that when these short chain fatty acids are metabolized, they provide energy and inhibit the synthesis of cholesterol. Therefore, indigestible substances are necessary in obtaining many desirable physiological effects.
As mentioned herein, digestion-resistant carbohydrate in dextrin (indigestible dextrin) is an important part of the human diet and provides several health benefits. However, the development of indigestible dextrin typically occurs contemporaneously with color development as the dextrinization reaction progresses. As starch is heated under altered conditions to obtain a higher indigestible starch content, the product increases the amount of colored substance, therefore, requiring purification.
In addition to high indigestible content, color is also often a major consideration in choosing a dextrin appropriate for a particular industrial application. Thus, the method of treatment that is used to produce indigestible dextrin depends directly on the intended application. For instance, a lack of brown color may be desirable in choosing a dextrin for use in paper adhesives, pharmaceutical, or food products, while brown dextrins may have more desirable tack and solubility characteristics.
Often times, it is preferable that the finished indigestible dextrin product be almost colorless in solution due to its application in the food industry. In the majority of cases, any color developed in the dextrinization process is not desirable in the final product and is largely removed through subsequent, and costly, decolorization steps. In order to minimize the costs associated with color removal, dextrins with minimal color development would be advantageous.
Thus, there is a need for bleached dextrins lacking in color with high indigestible starch content and methods of producing the same. The object is to manufacture a dextrin with the greatest degree of digestion-resistant carbohydrate possible while minimizing objectionable color formation.